Hybrid drivetrains are well known from series applications. In such cases, in addition to a combustion engine which drives a transmission input shaft, an electric machine is provided which serves as a generator in the deceleration phase of the drivetrain, and furthermore, in an electric-motor operating mode drives the combustion engine and/or the motor vehicle using the hybrid drivetrain alone or as support in combination with the combustion engine. In these cases, a friction clutch operates between the combustion engine and the electric machine, which uncouples these from each other.
In a special hybrid drivetrain, a freewheel is positioned between the crankshaft of the combustion engine and the transmission input shaft of the transmission, which is situated such that it blocks in the direction of transmission of torque from the combustion engine to the transmission, and rolls over in the drag direction. To be able to transmit drag torque to the combustion engine, for example, to decelerate the motor vehicle in addition to possible recovery of the electric machine, the friction clutch is at least partially engaged for this purpose. Furthermore, the friction clutch is engaged if the combustion engine is to be started in a cold or warm start by means of the electric machine, for example, when the motor vehicle is standing still, or while the motor vehicle is being propelled exclusively by means of the electric machine or is coasting. To this end, a starting torque, which is formed exclusively by the electric machine and/or from the kinetic energy of the motor vehicle, is transmitted via the friction clutch. The summed torque is therefore made up proportionately of drag torque and starting torque, and may far exceed the requisite torque necessary for starting the combustion engine or for supporting drag torque when the friction clutch is conventionally engaged, so that the components of the friction clutch, such as, for example, leaf springs, riveted joints, the clutch plate and the like, which are positioned between the pressure plate and the housing must be appropriately largely dimensioned. For example, when lining friction coefficients of the friction linings of the clutch plate change, especially high torques, which are unnecessary at this level can be transmitted.